The purpose of this study is to quantify total gluconeogenesis, the rate of lipolysis and triglyceride fatty acid cycling, and to estimate the contribution of glycerol to glucose. The populations to be studied are normal pregnant women, non-pregnant controls, and pregnant women with diabetes or growth retarded fetuses. We hypothesize that with advancing gestation, the increased fetal and maternal demands for carbohydrate energy are met by increasing hepatic gluconeogenesis, and that it will be further increased in diabetic pregnancy and decreased in women with growth retarded fetuses. Methods of study include the use of the stable isotopes [1,2,3-13C3] glycerol and [6,6-2H2] glucose, indirect respiratory calorimetry, and breath samples for 13C02 analysis. No side effects have been experienced.